Electrode for vapor discharge lamps



March 8, 1938. c. w. HUNT ELECTRODE FOR VAPOR DISCHARGE LAMPS Filed Dec.1, 1936 Mm. vwwL ATTORNEY Patented-Mar. 8,

UNITED STATES PATENT OFFICE ELECTRODE FOR. VAPOR msormnos LAMPSPennsylvania Application December 1, 1936, Serial No. 113,564

6 Claims.

My present invention relates to discharge devices and has particularreference to the electrode construction for lamps utilizing an ionizablemedium for supporting a discharge wherein starting of the discharge isfacilitated.

In lamps of this type it is customary to employ a vaporizable metal,such as mercury, sodium, cadmium or the like, which becomes vaporizedand supports the discharge. However, the vaporizable metal initially maybe in a solid state or have a vapor pressure so low as to not supportadischarge. Accordingly, it is customary to employ in addition to thevaporizable metal a small quantity of one or more rare gases tofacilitate starting of a discharge. During operation of these lamps thevapor pressure may be comparatively high but initially is much lower andrises with the temperature until the vaporizable metal is completelyvolatilized at which time maximum efficiency of the lamp is obtained.

Despite the filling of rare gas to facilitate starting it is quitediificult to initiate a discharge between the electrodes withoututilizing voltages considerably higher than the normal operatingvoltages. To overcome this disadvantage it has been the practice toemploy electrodes made of cores of alkaline earth compounds, such ascarbonates, hydroxides, or silicates with or without metal mixtures.Such cores are inserted in sections of highly refractory metal and theoxides activated by heating to a high temperature by the passage of anelectrical discharge or in some instances by high frequency inductionheating.

Although electrodes constructed in such manner, when energized by thepassage of an electrical current cause an initial discharge by reason ofthe deposit of electron emissive material, which becomes emissive evenat low temperature and pressure, together with initial ionization of therare gases, nevertheless such electrodes are subject to certain inherentdisadvantages. Since the electrodes are subjected to high temperatureand some bombardment during operation of the tube after volatilizationof the vaporizable metal, the oxide surface vaporizes and sputtersshortening the life of the tube and also causing a blackening of theenvelope.

It is accordingly an object of my present invention to provide animproved form of electrode for a high pressure vapor discharge device.

Another object of my present invention is the provision of an electrodeparticularly adaptable to high pressure discharge tubes wherein astarting electrode is so connected and positioned relative to the maindischarge supporting electrode as to supply a copious flow of electronsfor initially ionizing the gaseous medium within the tube and causing adischarge together with a rapid increase in the temperature so that amain discharge results in a comparatively short period of time betweenthe main electrodes.

A further object of my present invention is the provision of anelectrode comprising a helical winding having a portion thereof bentupon itself extending axially of the helix and provided with a furtherhelical windingwound transversely to the convolutions of the helixhaving a coating of high emissive electron material capable of emittingelectrons-at low temperatures, with the helical electrode positionedrearwardly of the main starting electrode and connected in electricalseries relationtherewith.

Still further objects of my present invention will become obvious tothose skilled in the art by reference to the accompanying drawingwherein:

Fig. 1 is a side elevational view of a discharge device including anelectrode constructed in accordance with my present invention, and

Fig. 2 is an enlarged sectional view taken on the line II--II of Fig. 1looking in the direction indicated by the arrows.

Referring to the drawing in detail I have shown in Fig. 1 a highpressure discharge tube comprising a sealed envelope 5 which isevacuated and sealed with a quantity of rare gas together with avaporizable metal such as mercury, sodium, cadmium or the like. Theenvelope 5 is provided at each end with a reentrant stem portion havinga press 6. Since the construction of the discharge device is identicalat both ends of the envelope, as is likewise the electrode, a detaileddescription of one should suffice. W

In accordance with my present invention a pair of supporting wires 1 and8 are's'ealed into the press 6 and connected to one of these supportingwires 1 is a leading-in conductor 9 extending from a suitable source ofelectrical potential (not shown) for the purpose of energizing the tubeduring operation. An operating electrode l0 composed of a. coil ofrefractory metal such as tungsten is connected to the extremities of thesupport wires 1 and 8soas to be suspended therebetween. In order tofacilitate starting of the discharge device without the necessity ofapplying a relatively high voltage thereto a starting electrode i2 ispositioned rearwardly of the operating electrode l0 and is thus disposedon the opposite side of the operating electrode to that from which thearc discharge strikes during operation of the device. The startingelectrode Ill l2 comprises substantially a helical winding of a coil ofrefractory metal such'as tungsten having a portion bent upon itselfpositioned at the axis of the helix. This electrode may be formed of acore of refractory metal and a winding of refractory metal is woundtransversely of the core. The ends of the starting electrode aresuitably connected to a rod or the like I3, such as by welding, and thisrod l3 may in turn be connected to the support wire 8 intermediate itsextremity and the press 6. A coating of high electron emissive materialis applied to the starting electrode I! so that a copious flow ofelectrons emanates from the electrode at comparatively low temperatures.

Accordingly'upon the initial application of a suitable voltage andcurrent from the source of supply (not shown) a discharge is initiatedbetween the oppositely disposed starting electrodes l2 owing to thecopious flow of electrons as previously stated which ionize the rare gasto initiate the discharge at relatively low temperatures.

Since the metallic vapor may be in a solid state or at a comparativelylow vapor pressure an appreciable time elapses before the temperature issufiiciently high to volatilize the vaporizable metal with an attendantincrease in the vapor pressure.

However, with my novel construction such time lapse is materiallyreduced, owing to the fact that the operating electrodes [0 are disposedtransversely to the longitudinal axis of the tube and between thestarting electrodes. In addition, since the starting electrodes l3 areconnected to the support wires 8, which later is merely imbedded in thepress 6 and consequently not connected directly to the leading-inconductor 9, the operating electrode l0 and starting electrode l2 arethus in electrical series relationship. In view of this arrangement theoperating electrodes ID are heated not only by the resulting initialdischarge between the starting electrodes l2 but in addition are heatedby the flow of current through the operating electrodes ID in passing tothe starting electrodes l2 to initiate the discharge. Thus the operatingelectrodes ID are heated very rapidly to a high temperature and this,together with the initiation of a discharge, likewise very rapidlyraises the temperature of the tube so that the volatilizable metalbecomes vaporized with an attendant increase in pressure followed by asustained arc discharge between the operating electrodes l0.

Upon the operating electrodes Ill assuming the discharge no furtherdischarge occurs between the starting electrodes with the result thatthey remain relatively cool during continued operation of the device.

Upon a deenergization of the device and a subsequent reenergizationthereof the cycle is repeated at which time the electrodes again operatein the manner just described until the temperature and pressure of thedevice has raised Y sufiiciently for the operating electrodes to takeover and sustain the operating discharge.

It can thus be readily seen by those skilled in the art that I haveprovided an electrode particularly adaptable to discharge devices of themetallic vapor type wherein the operating electrodes are disposedtransversely of the longitudinal axis of the device and are interposedbetween the starting electrodes, the later of which are provided with acoating of high electron emissive material.

Moreover, the operating electrodes are connected in series with thestarting electrodes so that the operating electrodes are heated veryrapidly not only by the initial discharge between the startingelectrodes but also by the flow of current through the operatingelectrodes. This arrangement not only facilitates the starting of thedevice, but the assumption of the discharge by the operating electrodesin a very short period of time, results in the starting electrodesremaining substantially cool during operation of the device. Also sincethe main discharge occurs in such a short period of time and thestarting electrodes are employed for such a short period of time, thiscontributes considerably to the longevity of the starting electrodes.

Although I have shown and described one specific improvement of mypresent invention, I do not desire to be limited thereto as variousother modifications thereof may be made Without departing from thespirit and scope of the appended claims.

What is claimed is:

1. An electric discharge device provided with a sealed envelope havingan ionizable medium therein, an operating electrode disposed at each endof said envelope and extending transversely of the latter, and ahelically wound starting electrode disposed rearwardly of each of saidoperat ing electrodes and axially directed toward each other with theiraxes perpendicular to that of said operating electrodes, and saidstarting electrodes being coated with a high electron emissive materialfor supplying a copious flow of electrons to initiate a discharge uponenergization of said device.

2. An electric discharge device provided with a sealed envelope havingan ionizable medium therein, an operating electrode disposed at each endof said envelope and extending in a direction transverse to thelongitudinal axis of said envelope, and a helically wound startingelectrode at each end of said envelope in back of said operatingelectrode having a coating of high electron emissive material, saidstarting electrodes being axially directed toward each other andoperable to initiate a discharge upon energization of said device.

3; An electric discharge device provided with a sealed envelope havingan ionizable medium therein, an operating electrode disposed at each endof said envelope and extending transversely to the longitudinal axis ofsaid envelope, and a helically wound starting electrode having a coatingof high electron emissive material disposed at each end of said envelopein back of said opthat-of said operating electrode, and said startingelectrodes being connected in electrical series with their adjacentoperating electrodes for the purpose of heating said operatingelectrodes by the resulting discharge between said starting electrodeswith the axis of the discharge being perpendicular to that of saidoperating electrodes and also for heating said starting electrodes bythe flow of current through said operating elec- 65 trodes to cause arapid rise in temperature upon energization of said device.

4. An electric discharge device provided with a sealed envelope havingan ionizable medium '55 erating electrode with its axis Pe pendicular toemissive material, and said starting electrodes being axially directedtoward each other and connected in electrical series relationship withtheir adjacent operating electrode in order that said operatingelectrodes are rapidly heated by the resulting initial discharge betweenthe starting electrodes and also by the flow of electrical currenttherethrough upon energization of said device.

5. An electric discharge device provided with a sealed envelope having areentrant press, a pair of'support wires sealed into said press andconnected to a leading-in conductor for supplying electrical energy tosaid device, an operating electrode supported by said support wireswithin said envelope with the axis thereof disposed transverse to thelongitudinal axis of said envelope, and a starting electrode disposedadjacent said operating electrode with its axis perpendicular tothe'latter and connected to one of said support wires for supportingsaid starting electrode and connecting the same in electrical seriesrelationship with said operating electrode.

6. An electric discharge device provided with a sealed envelope having areentrant press, a pair of support wires sealed into said press, aleadingin conductor connected to one of said support wires for supplyingelectrical energy to said device, an operating electrode within saidenvelope and suspended between said support wires at the extremitiesthereof, and a. helically wound starting electrode supported by saidsupport wire other than the one to which the said leading-in conductoris connected and intermediate said press and the extremity thereof.

CHARLES W. HUNT.

